In this specification, some embodiments of the invention will be described in terms of a process using fine particulate wastes containing iron values and which are generally referred to as steelworks dusts. In modern steelmaking such ferruginous dusts are produced particularly during oxygen steelmaking and electric steelmaking, the dust frequently containing significant zinc values. In some steel making plants, a wet process is used for removing the waste and the steelworks dusts are in the form of a sludge, but in this specification the term "steelworks dusts" will be used to cover the fine wastes from steelworks whether in dust form or sludge form. However, it is to be understood that the invention is not necessarily limited just to the processing of such steelworks dusts and analogous applications may exist. Other materials which may be used are ore, steel and iron scrap (which is finely divided to become a feedstock) and other ferrous particulates.
Generally steelworks are located in areas having substantial populations in the vicinity and accordingly having a major problem in dealing with sewage sludges, the disposal of which is often environmentally harmful. Sewage sludges may contain pathogens as well as harmful chemicals in small quantity, such as heavy metals and chlorinated and fluorinated hydrocarbons.
There is also a widespread problem in modern steelworks in dealing with the steelwork dusts. These dusts contain zinc oxide and spinels which result in the dust being unsuitable for return to sinter plants and from there back to blast furnaces since the zinc content creates problems to upper refractories in the shaft of a blast furnace. A large proportion of modern steelworks dusts are micron-sized particles mainly of iron and iron oxides in which the whole range of valencies of iron are represented. Furthermore the dusts usually contain a variety of calcium-containing compounds, zinc-containing compounds and carbon-containing compounds.
Thus, in many industrial areas around the world, there is a major problem of waste from ferrous metals industry, waste from sewage sludge and other carbon wastes (such as weed, paper waste and other sources), all of which present longstanding economic disposal problems. Land fill has become unavailable or very expensive and is often environmentally unacceptable, especially when the wastes, are contaminated.
Examples of prior published proposals are:
AUA 50854/73--Calspan Corporation PA1 AUB 403623--Conzinc Riotinto of Australia Limited PA1 AUB 403167--(equivalent U.S. Pat. No. 3,664,828) Conzinc Riotinto of Australia Limited PA1 AUB 404433--Worner PA1 JP 55-49200--Nippon Process Engineering KK PA1 U.S. Pat. No. 4,004,918--Fukuoka PA1 JP 58-156399--OTAT PA1 DE 3148550--Hamberger Stahlwerke GmbH PA1 JP 01-11700--Mitsubishi Mining & Cement Co Ltd PA1 U.S. Pat. No. 4,711,727--Matthews et al PA1 U.S. Pat. No. 4,793,855--Hauk PA1 U.S. Pat. No. 3,262,771--Ban PA1 U.S. Pat. No. 3,770,419--Brown PA1 U.S. Pat. No. 4,758,268--Bishop et al PA1 (a) The carbon in the composites has a fuel function as well as a chemical reduction function. PA1 (b) The excess carbon provides fuel values which can achieve high gas temperatures to provide the incineration role of the process as well as transferring heat back to the slag and molten metal. PA1 (c) The excess carbon provides fuel to maintain a relatively high bath temperature which facilitates a higher rate of smelting of the composites and absorption of surplus carbon into the metal in the bath. PA1 (d) The excess carbon provides fuel for ensuring high temperatures which cause zinc values to boil rapidly from the molten metal. The zinc leaves the bath as elemental metal and in the gas discharge oxidises to zinc oxide. PA1 Waste steelworks dusts can be processed to recover metal values thereby obviating storage or disposal problems and sewage can be processed to remove solids to leave cleaned water suitable for discharge or irrigation purposes; heavy metals, pathogens and organic chemicals of a potentially hazardous character often found in sewage will be removed for high temperature combustion whereby environmental contamination is obviated. PA1 The physical interaction of steelworks dusts and sewage can be an effective relatively rapid process permitting capital-effective processing plants to be constructed. PA1 An energy efficient process can be achieved utilising the energy values in the carbon contained in sewage sludge and metal of commercial value can be recovered in the smelting operation. PA1 The smelting operation can provide for high temperature combustion permitting safe disposal in addition of numerous other waste products.